390 research outputs found
Sequential Quantum Teleportation of Optical Coherent States
We demonstrate a sequence of two quantum teleportations of optical coherent
states, combining two high-fidelity teleporters for continuous variables. In
our experiment, the individual teleportation fidelities are evaluated as F_1 =
0.70 \pm 0.02 and F_2 = 0.75 \pm 0.02, while the fidelity between the input and
the sequentially teleported states is determined as F^{(2)} = 0.57 \pm 0.02.
This still exceeds the optimal fidelity of one half for classical teleportation
of arbitrary coherent states and almost attains the value of the first
(unsequential) quantum teleportation experiment with optical coherent states.Comment: 5page, 4figure
Experimental generation of four-mode continuous-variable cluster states
Continuous-variable Gaussian cluster states are a potential resource for
universal quantum computation. They can be efficiently and unconditionally
built from sources of squeezed light using beam splitters. Here we report on
the generation of three different kinds of continuous-variable four-mode
cluster states. In our realization, the resulting cluster-type correlations are
such that no corrections other than simple phase-space displacements would be
needed when quantum information propagates through these states. At the same
time, the inevitable imperfections from the finitely squeezed resource states
and from additional thermal noise are minimized, as no antisqueezing components
are left in the cluster states.Comment: 5 pages, 4 figure
Bipolar diathermy for the outpatient control of posterior epistaxis
LetterThe original publication is available at http://www.samj.org.za[No abstract available
Quantum versus classical domains for teleportation with continuous variables
By considering the utilization of a classical channel without quantum entanglement, fidelity Fclassical=1/2 has been established as setting the boundary between classical and quantum domains in the teleportation of coherent states of the electromagnetic field [S. L. Braunstein, C. A. Fuchs, and H. J. Kimble, J. Mod. Opt. 47, 267 (2000)]. We further examine the quantum-classical boundary by investigating questions of entanglement and Bell-inequality violations for the Einstein-Podolsky-Rosen states relevant to continuous variable teleportation. The threshold fidelity for employing entanglement as a quantum resource in teleportation of coherent states is again found to be Fclassical=1/2. Likewise, violations of local realism onset at this same threshold, with the added requirement of overall efficiency η>2/3 in the unconditional case. By contrast, recently proposed criteria adapted from the literature on quantum-nondemolition detection are shown to be largely unrelated to the questions of entanglement and Bell-inequality violations
Practical effects in the preparation of cluster states using weak non-linearities
We discuss experimental effects in the implementation of a recent scheme for
performing bus mediated entangling operations between qubits. Here a bus mode,
a strong coherent state, successively undergoes weak Kerr-type non-linear
interactions with qubits. A quadrature measurement on the bus then projects the
qubits into an entangled state. This approach has the benefit that entangling
gates are non-destructive, may be performed non-locally, and there is no need
for efficient single photon detection. In this paper we examine practical
issues affecting its experimental implementation. In particular, we analyze the
effects of post-selection errors, qubit loss, bus loss, mismatched coupling
rates and mode-mismatch. We derive error models for these effects and relate
them to realistic fault-tolerant thresholds, providing insight into realistic
experimental requirements.Comment: 8 pages, 5 figure
Quasiprobability methods for multimode conditional optical gates
We present a method for computing the action of conditional linear optical
transformations, conditioned on photon counting, for arbitrary signal states.
The method is based on the Q-function, a quasi probability distribution for
anti normally ordered moments. We treat an arbitrary number of signal and
ancilla modes. The ancilla modes are prepared in an arbitrary product number
state. We construct the conditional, non unitary, signal transformations for an
arbitrary photon number count on each of the ancilla modes.Comment: 6 pages, 2 figures. JOSA B Special Issue "Optical Quantum Information
Science
Axillary nodal metastasis at primary presentation of an oropharyngeal primary carcinoma: a case report and review of the literature
<p>Abstract</p> <p>Introduction</p> <p>Axillary nodal metastasis is very rare in head and neck squamous cell carcinoma. The few cases reported in the literature all involve patients who have previously undergone either neck dissection alone, or neck dissection and radiotherapy to the neck, and subsequently develop delayed recurrences of disease, with axillary nodal involvement.</p> <p>Case presentation</p> <p>We present the case of a 62-year-old man of Cape Malay ethnicity, who presented with an oropharyngeal squamous cell carcinoma, and cervical and axillary nodal metastasis at primary presentation.</p> <p>Conclusion</p> <p>Whilst previous reports in the literature suggest routine examination of the axilla is advisable in patients with previously treated neck cancer and recurrence of head and neck cancer, we propose that the axilla should be routinely examined in new cases, particularly when there is involvement of the level 5 nodes.</p
Experiment towards continuous-variable entanglement swapping: Highly correlated four-partite quantum state
We present a protocol for performing entanglement swapping with intense
pulsed beams. In a first step, the generation of amplitude correlations between
two systems that have never interacted directly is demonstrated. This is
verified in direct detection with electronic modulation of the detected
photocurrents. The measured correlations are better than expected from a
classical reconstruction scheme. In the entanglement swapping process, a
four--partite entangled state is generated. We prove experimentally that the
amplitudes of the four optical modes are quantum correlated 3 dB below shot
noise, which is due to the potential four--party entanglement.Comment: 9 pages, 10 figures, update of references 9 and 10; minor
inconsistency in notation removed; format for units in the figures change
Hybrid quantum repeater using bright coherent light
We describe a quantum repeater protocol for long-distance quantum
communication. In this scheme, entanglement is created between qubits at
intermediate stations of the channel by using a weak dispersive light-matter
interaction and distributing the outgoing bright coherent light pulses among
the stations. Noisy entangled pairs of electronic spin are then prepared with
high success probability via homodyne detection and postselection. The local
gates for entanglement purification and swapping are deterministic and
measurement-free, based upon the same coherent-light resources and weak
interactions as for the initial entanglement distribution. Finally, the
entanglement is stored in a nuclear-spin-based quantum memory. With our system,
qubit-communication rates approaching 100 Hz over 1280 km with fidelities near
99% are possible for reasonable local gate errors.Comment: title changed, final published versio
Quantum Repeaters using Coherent-State Communication
We investigate quantum repeater protocols based upon atomic
qubit-entanglement distribution through optical coherent-state communication.
Various measurement schemes for an optical mode entangled with two spatially
separated atomic qubits are considered in order to nonlocally prepare
conditional two-qubit entangled states. In particular, generalized measurements
for unambiguous state discrimination enable one to completely eliminate
spin-flip errors in the resulting qubit states, as they would occur in a
homodyne-based scheme due to the finite overlap of the optical states in phase
space. As a result, by using weaker coherent states, high initial fidelities
can still be achieved for larger repeater spacing, at the expense of lower
entanglement generation rates. In this regime, the coherent-state-based
protocols start resembling single-photon-based repeater schemes.Comment: 11 pages, 8 figure
- …